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Assessment of ambient air quality

The Ambient Air Quality Directives require the assessment of the ambient air quality in Member States based on common methods and criteria for air quality monitoring and modelling. This comprehensive assessment is required throughout the whole territory of each country. The assessments should be done in a way so that they are representative of other locations. Find out more on spatial representativeness.

When air quality monitoring is being used for air quality assessment, it is extremely important to appropriately site sampling points. This ensures monitoring information can be used to obtain further information on

  • exposure
  • source apportionment that supports the development of air policy
  • and air pollution management in the area

Key provisions

Amongst other key provisions, Directive 2008/50/EC

  1. Requires that a minimum of one rural background station is installed every 100 000 km2 for measuring PM2.5 in order to get data on the total mass concentration and the chemical speciation. See the Guidelines for more information.
  2. Allows Member States to subtract the contribution of natural sources under certain conditions before comparing the ambient air pollutant concentrations to the limit values. See the Guidelines and an assessment study performed in 2022 for more information.
  3. Indicates that for designated zones or agglomerations within which limit values for PM10 are exceeded in ambient air, such exceedance is due to the re-suspension of particulates following winter sanding or salting of roads. See the Guidelines for more information.


Reference air quality measurement methods

For each regulated pollutant, a reference measurement method has been prescribed. At the time of the adoption of the directives, standardised methods had not been developed for all pollutants. The situation has since developed, and an updated list of reference measurement method is available, explicitly referenced in the Ambient Air Quality Directives:

  • SO2: EN 14212:2012
  • NO2 and NOx: EN 14211:2012
  • Pb, Cd, As, Ni: EN 14902: 2005
  • PM2.5/PM10: EN 12341:2014
  • Benzene: EN 14662:2005
  • CO: EN 14626:2012
  • OC/EC: EN16909: 2017

The standards can be obtained through the national standardisation organisation. See also:

Non-reference measurement methods can also be used provided they respect provisions for equivalence set out in the Directives (see for example 2008/50/EC, Annex VI). A Commission Working Group on Equivalence has prepared a document describing principles and methodologies to be used to demonstrate the equivalence of alternative (non-reference) measurement methods to the reference methods described by the EN Standard methods:

The corresponding tool to facilitate the use of the guidance (in particular for checking the equivalence of non-reference methods for PM-monitoring) has been developed. The updated version is now available:

The previous version is available here:

The template provides the formulas and macros with the statistical calculations needed and includes a tutorial on how to use the tool.

Air quality modelling

Air quality modelling is considered to provide supplemental information to air quality monitoring. It can provide more comprehensive information on public exposure, and supports identification of sources and future projections based on different measures scenarios.

A Forum for AIR quality MODElling (FAIRMODE) of modellers and users has been established. The aim of the Forum is to support the widespread and harmonised use of models through model validation and intercomparison exercises and through the management of the modelling network. The FAIRMODE webpage contains links to current activities.

Objective estimation of air quality

The Ambient Air Quality Directives also allow for objective estimation as an air quality assessment method for air quality zones with very good air quality and no large conurbations. By identifying local pollution sources and information on regional air quality, an estimation of concentration of a regulated pollutant is made.

Ensuring quality of air quality assessment information

Ensuring quality of assessment information either generated through monitoring, modelling or objective estimation is one of the paramount provisions of the directives. Data quality objectives are prescribed which define maximum allowed uncertainty, time coverage and data coverage.

Member States are responsible for ensuring appropriate quality assurance of the assessment as well as the appropriate quality control of the information provided to the public and through the assessment reports. The Commission has set-up a community-wide process, managed by the Joint Research Centre (JRC).

AQUILA is a network of national reference laboratories that provides expert advice to the Commission. It has prepared an extensive document that summarises the roles and responsibilities of the national reference laboratories and of the network itself, describes the quality assurance procedures and makes EU-wide comparisons.

The European Environment Agency (EEA) together with EIONET and its Topic Centre also supports quality assurance of the data and reporting of air quality assessment information.